Image forming apparatus, method for controlling image forming apparatus, and non-transitory computer readable medium

ABSTRACT

An image forming apparatus includes a storage unit storing sheets each including a wireless tag, a printer, a communication device, and a controller for controlling the printer to convey a first sheet, acquiring first strengths of signals from a first tag on a first sheet during the conveyance of the first sheet and second strengths from tags not sheets being conveyed. Based on the acquired strengths, the controller determines a threshold value for distinguishing between sheets being conveyed and not being conveyed. The controller then controls the communication device to write information to a tag on a sheet being conveyed based on the threshold value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2020-011480, filed on Jan. 28, 2020, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an image formingapparatus, a method for controlling the image forming apparatus, and anon-transitory computer readable medium.

BACKGROUND

There is an image forming apparatus capable of forming an image on asheet on which a wireless tag is provided. Such an image formingapparatus has a wireless tag communication device that writesinformation to the wireless tag and a sheet storage unit in which thesheet can be stored, such as a sheet feeding cassette and a manualfeeding tray.

The wireless tag communication device may intend to write information toa wireless tag on a sheet that has been conveyed from the storage unitand is being conveyed for printing or other processing. However, due tothe relatively close proximity of the wireless tag communication deviceto the storage unit (and the sheets therein), the wireless tagcommunication device may unintentionally write information to a wirelesstag provided on a sheet still in the storage unit rather than one on asheet being conveyed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an image forming apparatus according to anembodiment.

FIG. 2 is a functional block diagram of an image forming apparatusaccording to an embodiment.

FIG. 3 is a diagram illustrating an example of a position where a sheetcan be present in an image forming apparatus.

FIG. 4 is a diagram showing changes in signal strength from a wirelesstag.

FIG. 5 is a flowchart of a threshold determination process performed byan image forming apparatus.

FIG. 6 is a flowchart of an image forming wireless tag control processperformed by an image forming apparatus during image formation.

FIG. 7 is a diagram showing changes in signal strength from a wirelesstag.

FIG. 8 is a diagram illustrating changes in signal strength from twowireless tags.

FIG. 9 is a flowchart of a threshold determination process performed byan image forming apparatus.

DETAILED DESCRIPTION

According to one embodiment, an image forming apparatus, include a firstsheet storage unit in which a plurality of sheets each with a wirelesstag can be stored, a printer unit configured to convey a sheet along aconveyance path, a wireless tag communication device configured tocommunicate with wireless tags, and a controller. The controller isconfigured to: control the printer unit to convey a first sheet alongthe conveyance path for image formation, control the wireless tagcommunication device to detect a plurality of radio signal strengthsfrom the first wireless tag during the conveyance of the first sheet anda plurality of radio signal strengths for wireless tags of sheets notbeing conveyed by the printer unit, determine a threshold value of radiosignal strength for distinguishing a wireless tag on a sheet beingconveyed along the conveyance path from wireless tags on sheets notbeing conveyed along the conveyance path based on the detected pluralityof radio signal strengths from the first wireless tag and the detectedplurality of radio signal strengths for wireless tags on sheets notbeing conveyed by the printer unit, and control the printer unit toconvey a second sheet and control the wireless tag communication deviceto write to a second wireless tag on the second sheet when a radiosignal strength from the second wireless tag is to equal or exceeds thethreshold value.

In an image forming apparatus of one or more embodiments, it is possibleto prevent erroneous writing of information to a wireless tag that isstored in or on the sheet storage unit and is on a sheet that is notbeing conveyed. Hereinafter, an image forming apparatus according tocertain example embodiments will be described with reference to thedrawings. In the following description, the same reference numerals aregiven to configurations having the same or substantially similarfunction. In addition, description of these overlapping configurationalaspects may be omitted in some cases.

First, a side view of an image forming apparatus 10 according to anembodiment will be described with reference to FIG. 1.

In FIG. 1, the image forming apparatus 10 includes a control panel 13, awireless tag communication device 201, and a printer unit 18. Theprinter unit 18 includes a controller 100, a sheet feeding cassette 16a, and a sheet feeding cassette 16 b, a manual feed tray 16 c, and thelike. The controller 100 controls the control panel 13, the wireless tagcommunication device 201, and the printer unit 18. The controller 100controls conveyance of a sheet in the printer unit 18. The control ofthe conveyance includes the control of a conveyance timing of the sheet,a stop position of the sheet, a conveyance speed of the sheet, and thelike.

The control panel 13 includes an input key and a display unit. Forexample, the input key accepts an input by a user. For example, thedisplay unit includes a touch panel. The display unit receives an inputfrom a user and displays information corresponding to the input to theuser. For example, the control panel 13 displays information related tosettings for the image forming apparatus 10 so that the user is able toconfirm and modify them. The control panel 13 notifies the controller100 of the settings specified by the user.

The sheet feeding cassettes 16 a and 16 b can each store a sheetincluding a wireless tag or a sheet to which a wireless tag is attached.The sheet feeding cassettes 16 a and 16 b can also store a regular sheetnot including a wireless tag. In the following description, unlessotherwise specified, the sheet having a wireless tag is used. Forexample, the sheet is made of a material such as paper, plastic film, orthe like.

The printer unit 18 performs an image forming operation. For example,the printer unit 18 forms an image on a sheet based on the image data.In the following description, forming an image on a sheet will also bereferred to as printing. The printer unit 18 includes an intermediatetransfer belt 21. The intermediate transfer belt 21 is supported by adriven roller 41, a backup roller 40, and the like in the printer unit18. The printer unit 18 rotates the intermediate transfer belt 21 in thedirection indicated by the arrow m.

The printer unit 18 includes four sets of image forming units 22Y, 22M,22C, and 22K. The image forming units 22Y, 22M, 22C, and 22K arerespectively used for image formation of different colors, Y (yellow), M(magenta), C (cyan), and K (black). The image forming units 22Y, 22M,22C and 22K are arranged on a lower side of the intermediate transferbelt 21 along a rotation direction of the intermediate transfer belt 21.

Hereinafter, the image forming unit 22Y (yellow) among the image formingunits 22Y, 22M, 22C, and 22K will be described as an example. The imageforming units 22M, 22C and 22K each have the same configuration as thatof the image forming unit 22Y, and description of image forming unit 22Yis therefore sufficient description of the other image forming units.

The image forming unit 22Y includes a photosensitive drum 24, a chargingunit 26, an exposure scanning head 27, a developing device 28, a cleaner29, and a primary transfer roller 30. The charging unit 26, the exposurescanning head 27, the developing device 28, and the cleaner 29 aredisposed around the photosensitive drum 24 that rotates in the directionof the arrow n.

The primary transfer roller 30 faces the photosensitive drum 24 via theintermediate transfer belt 21.

The image forming unit 22Y electrostatically charges the photosensitivedrum 24 using the charging unit 26 and selectively exposes thephotosensitive drum 24 to light from the exposure scanning head 27, andthereby forms an electrostatic latent image on the photosensitive drum24. The developing device 28 develops the electrostatic latent image onthe photosensitive drum 24 by using a two-component developer formed bytoner and carrier.

The primary transfer roller 30 transfers the toner image formed on thephotosensitive drum 24 to the intermediate transfer belt 21 (hereinafterreferred to as the “primary transfer”). Each of the image forming units22Y, 22M, 22C and 22K forms a different color toner image on theintermediate transfer belt 21 by the corresponding primary transferroller 30. The color toner images are formed by sequentially stackingtoner images of Y (yellow), M (magenta), C (cyan), and K (black). Thecleaner 29 removes the toner remaining on the photosensitive drum 24after the primary transfer.

The printer unit 18 includes a secondary transfer roller 32. Thesecondary transfer roller 32 faces the backup roller via theintermediate transfer belt 21. The secondary transfer roller 32transfers the color toner images on the intermediate transfer belt 21 tothe sheet (hereinafter referred to as the “secondary transfer”). In thefollowing description, the term “toner image” may refer to a color tonerimage or a single color toner image. The toner image may be a tonerimage using a decolorable toner.

A conveyance path 33 a extends from a merging portion 44 a to a branchportion 44 b. A conveyance path 33 b passes through the inside of adouble-sided printer 38 and extends from the branch portion 44 b to themerging portion 44 a. A conveyance path 33 c extends from the branchportion 44 b to a sheet discharge tray 20.

The leading end of a sheet taken out from the sheet feeding cassette 16a, the sheet feeding cassette 16 b, or the manual feed tray 16 c abutsagainst a portion where two registration rollers 31 are in contact witheach other. The inclination of the sheet is corrected when the leadingend contacts the registration rollers 31. The controller 100 rotates theregistration rollers 31 in accordance with the position of the tonerimage of the rotating intermediate transfer belt 21, and moves the sheetto the position of the secondary transfer roller 32. The controller 100secondarily transfers the toner image formed on the intermediatetransfer belt 21 to the sheet by the secondary transfer roller 32. Thecontroller 100 causes the sheet to be conveyed along the conveyance path33 a, and control a fixing device 34 to fix the toner image to thesheet. The controller 100 causes the sheet on which the image has beenformed to be conveyed along the conveyance path 33 c and discharged tothe sheet discharge tray 20.

In the case of double-sided printing, the controller 100 also causes thesheet on which the image has been formed on the front side to beconveyed along the conveyance path 33 c. But after the entire sheetpasses through the branch portion 44 b, the controller 100 causes thesheet to be conveyed back along the conveyance path 33 b (i.e., switchback). Then, the controller 100 causes the sheet to proceed to themerging portion 44 a along the conveyance path in the double-sidedprinter 38, and then again conveyed along the conveyance path 33 a viathe registration roller 31. Then, the controller 100 controls the fixingdevice 34 to fix the toner image on the back surface of the sheet. Thecontroller 100 causes the sheet on which the image has been formed onthe back side to be conveyed along the conveyance path 33 c anddischarged to the sheet discharge tray 20.

The wireless tag communication device 201 includes a processor and astorage device. The wireless tag communication device 201 is capable ofcommunicating with the controller 100. The wireless tag communicationdevice 201 reads information from a wireless tag or writes informationto the wireless tag by communicating with the wireless tag of the sheet.In one embodiment, the wireless tag is a radio frequency identifier(RFID) tag, and the wireless tag communication device 201 is an RFID tagreader/writer. As shown in FIG. 1, the wireless tag communication device201 transmits radio waves in the arrow k direction. The wireless tagcommunication device 201 measures a received power strength of the radiowave transmitted from the wireless tag, and transmits the detectedreceived power strength to the controller 100. In one embodiment, thepower strength is represented by a received signal strength indicator(RSSI). In the following description, “RSSI of a wireless tag” indicatesthe RSSI of the radio wave transmitted from the wireless tag, and “RSSIof a sheet” indicates the RSSI of the radio wave transmitted from thewireless tag provided in/on the sheet.

In the printer unit 18, an electrostatic latent image is formed on thephotosensitive drum 24 by the exposure scanning head 27 before thesecondary transfer is performed by the secondary transfer roller 32. Theelectrostatic latent image formed on the photosensitive drum 24 isprimarily transferred to the intermediate transfer belt 21 as a tonerimage. Further, by the secondary transfer roller 32, the toner image issecondarily transferred to a sheet that has been conveyed to theposition of the registration roller 31.

Next, a functional block diagram of the image forming apparatus 10according to an embodiment will be described with reference to FIG. 2.

In FIG. 2, the image forming apparatus 10 includes the controller 100,the control panel 13, the printer unit 18, and the wireless tagcommunication device 201.

The controller 100 includes a processor 51, a memory 52, a communicationinterface 53, and a data conversion unit 54. The processor 51 controlsthe control panel 13, the printer unit 18, and the wireless tagcommunication device 201 in accordance with an image processing programstored in the memory 52.

The processor 51 is, for example, a central processing unit (CPU), anapplication specific integrated circuit (ASIC), or the like. The memory52 includes a read only memory (ROM), a random access memory (RAM), ahard disk drive (HDD), and/or a solid state drive (SSD). Thecommunication interface 53 is an interface to receive print data (forexample, data described in a page description language) indicating animage to be printed from a host such as a personal computer (PC). Thereceived print data is stored in the memory 52. The image dataconversion unit 54 determines a print condition based on the print datastored in the memory 52, and converts the print data into a printabledata format (for example, raster data) that can be used by the printerunit 18, and stores the converted data in the memory 52.

The printer unit 18 includes the fixing device 34, the secondarytransfer roller 32, and the developing device 28. The printer unit 18forms an image on a sheet based on the data converted by the image dataconversion unit 54.

Next, a description will be given of a control for preventing erroneouswriting of information to a non-target wireless tag other than a targetwireless tag. FIG. 3 is a diagram illustrating various positions where asheet can be present in the image forming apparatus 10. In FIG. 3, thesheet S1 is a sheet in the sheet feeding cassette 16 a. The sheet S2 isa sheet on the sheet discharge tray 20. The sheet S3 is a sheet on themanual feed tray 16 c. The sheet feeding cassettes 16 a and 16 b, thesheet discharging tray 20, and the manual feeding tray 16 c are examplesof the sheet storage unit.

The sheet S0 is a sheet that is being conveyed through the conveyancepath 33 a. The sheets S0, S1, S2, and S3 have wireless tags T0, T1, T2,and T3, respectively.

In an embodiment, a sheet in which information is written to thewireless tag (hereinafter, also referred to as a “target sheet”) isbeing conveyed along the conveyance path 33 a.

In FIG. 3, the wireless tag communication device 201 transmits radiowaves in the arrow k direction. Each wireless tag that has received theradio wave responds (returns radio waves) to the wireless tagcommunication device 201. The wireless tag communication device 201receives radio waves from the wireless tags of each sheet. The RSSI ofeach wireless tag varies depending on the distance from the wireless tagcommunication device 201, the directionality of the radio wave, theinterposition of device components between the tag, and the like.

In this example, the sheets S1, S2, and S3 are not presently beingconveyed, whereas the sheet S0 is being conveyed. Therefore, while thesheet S0 is being conveyed, the RSSI of each of the immobile wirelesstags T1, T2, and T3 does not change, but the RSSI of the wireless tag T0changes.

In an embodiment, the timing for the writing of information to thewireless tag is controlled based on the RSSI detected when the targetsheet is being conveyed. In the present disclosure, two non-limitingexamples will be described for the control of the writing. In theseexamples, the controller 100 acquires a threshold of RSSI fordistinguishing the wireless tag of a target sheet (a sheet beingconveyed) from the other wireless tags of the sheets still stored in thesheet storage unit. When a RSSI of a wireless tag is within a rangedetermined by the threshold, the controller 100 determines that thesheet with the wireless tag is being conveyed and controls the wirelesstag communication device 201 to write information to the wireless tag.In the following description, the RSSI of the wireless tag TX (whereX=0, 1, 2, or 3) may be expressed as R(X). For example, the RSSI of thewireless tag T0 is expressed as R(0).

First Embodiment

In a first embodiment, R(1), R(2), R(3), and R(0) are compared with eachother. FIG. 4 is a diagram illustrating the values for R(0), R(1), R(2),and R(3) detected by the wireless tag communication device 201 while thetarget sheet is being conveyed. In the graph shown in FIG. 4, thehorizontal axis represents time, and the vertical axis represents RSSI.The detection of the RSSI by the wireless tag communication device 201is performed at a particular fixed interval or the like.

A sheet (S0) is conveyed from the sheet feeding cassette 16 a and thenultimately discharged to the sheet discharge tray 20. Therefore, R(0)initially increases from the same value as R(1). R(0) reaches themaximum value (P) while being conveyed in the conveyance path 33 a, andthen gradually decreases. When the sheet is finally conveyed to thesheet discharge tray 20, R(0) has the same value as that of the R(2).

The controller 100 determines a threshold value TH of RSSI within arange [R(1), P]. That is, the threshold value is greater than themaximum RSSI of the sheets not being conveyed and equal to or less thanthe maximum value P. An example of the determination method will bedescribed later. The threshold TH allows the controller 100 todistinguish between the wireless tag of a target sheet and the wirelesstags of the other non-target sheets.

The controller 100 determines the threshold TH by conveying one sheet inadvance. Then, the controller 100 causes another sheet to be conveyed,and when a detected RSSI value falls within a range defined by thethreshold value during image formation, the controller 100 controls thewireless tag communication device 201 to write information to thewireless tag. In the example of FIG. 4, the “range determined by thethreshold” is a range [TH, +∞], i.e., greater than or equal to thethreshold TH. In actual control, the controller 100 controls thewireless tag communication device 201 to write information to a wirelesstag when a detected RSSI is greater than or equal to the threshold THfor the wireless tag.

By starting the writing to the wireless tag at the time when thedetected RSSI has just reached the threshold TH, it is possible tosecure as much time as possible for completing the tag writing process,which suppresses the occurrence of an error, such as a write failure.Further, the efficiency of printing can also be improved by choosing asmaller threshold and increasing the conveyance speed of the sheet.

The range defined by the threshold TH described above includes any RSSIgreater than or equal to the threshold TH. Further, the range does notinclude any RSSI detected from the wireless tags of sheets stored in thesheet storage unit. Thus, it is possible to prevent erroneous writing ofinformation to the wireless tags other than the target wireless tag.

The above-described control will be described with reference to aflowchart. FIG. 5 is a flowchart of the threshold determinationprocessing carried out by the controller 100. In order to convey atarget sheet, the controller 100 transmits a conveyance start command tothe printer unit 18 (ACT101). The controller 100 acquires RSSIs detectedby the wireless tag communication device 201 via the communicationinterface 53 (ACT102). Here, the RSSIs R(0), R(1), R(2), and R(3) areobtained. The controller 100 associates the time elapsed after thetransmission of the conveyance start command with the acquired RSSIs,and stores the acquired RSSIs in the memory 52.

The controller 100 determines whether the conveyance of the target sheethas been completed (ACT104). When the conveyance is completed, a messageindicating that the conveyance has ended is transmitted from the printerunit 18 to the controller 100. The controller 100 can determine whetherthe conveyance of the target sheet has been completed depending onwhether the message is received.

If the conveyance has not ended (ACT104: NO), the controller 100continues to acquire the RSSIs in ACT102. If the conveyance is completed(ACT104: YES), the controller 100 determines a threshold (ACT105),stores the determined threshold in the memory 52 (ACT106), and ends theprocessing. As described above, ACT102 and ACT103 can be repeated untilthe sheet conveyance is completed. Therefore, a plurality of RSSIs R(0),R(1), R(2), and R(3) are acquired during a sheet conveyance. Forexample, the acquisition of the RSSIs is repeated for ten times, but theacquisition may be repeated for any number of times according to thevariation of the RSSI.

A method for determining the threshold will be described. Here, theaverage values of a plurality of R(0), R(1), R(2), and R(3) valuesacquired are respectively referred to as AvR(0), AvR(1), AvR(2), andAvR(3). Once R(0), R(1), R(2), and R(3) have been repeatedly acquired,the controller 100 calculates each average value, AvR(0), AvR(1),AvR(2), and AvR(3). The controller 100 next determines max(AvR(1),AvR(2), and AvR(3)) and takes this maximum value as the maximum value M1of which corresponds to the maximum RSSI of the wireless tags of thesheets still in a sheet storage unit. Additionally, the controller 100determines a maximum value M2 of R(0) (M2=max(R(0)).

The controller 100 calculates an average value of the maximum values M1and M2 (average value=(M1+M2)/2). The controller 100 sets thiscalculated average value as the threshold TH. The method of setting sucha simple average value as the threshold TH can be performed with arelatively small processing load. In another calculation method,expected variations in RSSI due to the individual characteristics of awireless tag or the like can be considered in calculating the thresholdTH.

The method for determining the threshold is not limited to the methoddescribed above, and, in general, any determination method may beemployed as long as the method enables the controller 100 to distinguishbetween the wireless tag of the target sheet and the wireless tags ofthe other non-target sheets.

The determined threshold TH is used during printing. FIG. is a flowchartof the wireless tag control processing during image formation carriedout by the controller 100. In order to start image formation, thecontroller 100 transmits an image forming start command to the printerunit 18 (ACT201). The controller 100 acquires the RSSI of a wireless tag(e.g., R(0)) as detected by the wireless tag communication device 201through the communication interface 53 (ACT202).

The controller 100 determines whether R(0) is greater than or equal tothe threshold TH (that is, is R(0)≥threshold TH satisfied?) that hasbeen determined by the method shown in FIG. 5 (ACT203). Therefore, inACT203, it is determined whether R(0)≥threshold TH has been satisfied.If R(0) is the threshold TH or more (ACT203: YES), the controller 100writes information (ACT205) into the wireless tag corresponding to R(0)that has been detected, and ends the processing.

If R(0) is not within the appropriate range(ACT203: NO), the controller100 next identifies whether the image formation process has beencompleted (ACT204). When the image formation has been completed, amessage indicating that the image formation has been completed istransmitted from the printer unit 18 to the controller 100. Thecontroller 100 can determine whether the image forming has beencompleted based on whether the message has been received.

If the image formation has not been completed (ACT204: NO), thecontroller 100 acquires R(0) again in ACT202. When the image formationis completed (ACT204: YES), the controller 100 ends the processing.

In the above-described wireless tag control processing during imageforming, information is written to a wireless tag only when an RSSIgreater than or equal to the threshold TH is detected, and thus it ispossible to prevent erroneous writing of the information to a non-targetwireless tag.

In the graph illustrated in FIG. 4, the maximum value of R(0) is greaterthan any other values of R(1), R(2), and R(3). However, the presentdisclosure can be applied to a case where the maximum value of R(0) isless than some of the values of R(1), R(2), or R(3) at various points.Specifically, description of this case will be made with reference toFIG. 7.

FIG. 7 is a diagram illustrating R(0), R(1), R(2), and R(3) as detectedby the wireless tag communication device 201 when a sheet is conveyed.In FIG. 7, it is assumed that the sheet is conveyed from the manual feedtray 16 c and then discharged to the sheet discharge tray 20. In thisexample, R(0) increases from the same value as R(3), then reaches themaximum value (P) while the sheet is being conveyed along the conveyancepath 33 a, and then begins to decrease. When the sheet has been finallyconveyed to the sheet discharge tray 20, then R(0) has the same value asthat of the R(2).

Thus, in this example, R(0) does not ever exceed the value of R(1) andonly exceeds the value of R(3) for a portion of the conveyance time. Toaccount for this, the controller 100 calculates two thresholds TH1 andTH2. Here, TH1 is P+a, and TH2 is P−b, where a and b are positive andare values satisfying P+a<R(1) and P−b>R(3).

The controller 100 calculates the thresholds TH1 and TH2 by conveyingone target sheet as a test sheet beforehand or the like. Then, thecontroller 100 controls the wireless tag communication device 201 towrite information to the wireless tag when the acquired RSSI fallswithin the range defined by the thresholds TH1 and TH2. In the exampleof FIG. 7, the “range determined by the thresholds” is range[TH2, TH1],that is, greater than or equal to the threshold TH2 and less than orequal to the threshold TH1. In actual control, the controller 100controls the wireless tag communication device 201 to write informationto a wireless tag when an RSSI greater than or equal to the thresholdTH2 and less than or equal to the threshold TH1 is detected from thewireless tag.

By starting the writing to the target wireless tag at the timing whenthe detected RSSI falls within the range [TH2, TH1], it is possible tosecure as much time as possible for completing the writing, whichsuppresses the occurrence of an error, such as a write failure. Further,the efficiency of printing can also be improved by choosing smallerthresholds and increasing the conveyance speed of the sheet.

As described above, in the first embodiment, by comparing signalstrengths from wireless tags R(1), R(2), R(3) and R(0) at variouspositions in the image forming apparatus 10, it is possible to preventinformation from being erroneously written to non-target wireless tags.

Second Embodiment

In a second embodiment, a plurality of sheets are conveyed to determinea threshold based on RSSIs received from the wireless tag provided ineach of the sheets being conveyed. Specifically, R(0) is acquired fromeach sheet being conveyed to determine the threshold. In the followingdescription, for illustration purpose, an example in which two sheetsare conveyed will be described.

FIG. 8 is a diagram illustrating two R(0) detected by the wireless tagcommunication device 201 when two sheets are conveyed in sequence. Inthe graph shown in FIG. 8, the horizontal axis represents time, and thevertical axis represents RSSI. The detection of the RSSI by the wirelesstag communication device 201 is performed at a particular interval orthe like.

As shown in FIG. 8, it is assumed that the maximum value of the RSSIs ofthe first sheet is P1, and the maximum value of the RSSIs of the secondsheet is P2 (where, in this example, P2>P1). The controller 100determines two thresholds TH3 and TH4, where TH3 is P2+c, and TH4 isP1−d, where c and d are positive and are values for accounting forvariations of the RSSI sheet to sheet (or more particularly wireless tagto wireless tag). In the example, the values of c and d are determinedin advance based on, for example, the known characteristics of thewireless tag, the obtained statistics of the variation in the RSSI, andthe like.

Similar to that described above, the controller 100 determines thethresholds TH3 and TH4 from the maximum values of RSSIs detected fromthe respective two sheets conveyed in sequence. Then, the controller 100controls the wireless tag communication device 201 to write informationto a wireless tag when the detected RSSI falls within the range definedby the thresholds TH3 and TH4. In the example of FIG. 8, the “rangedetermined by the threshold” is a range [TH4, TH3], i.e., greater thanor equal to the threshold TH4 and less than or equal to the thresholdTH3. In the actual control, the controller 100 controls the wireless tagcommunication device 201 to write information to a wireless tag when anRSSI (R(0)) is greater than or equal to the threshold TH4 and less thanor equal to the threshold TH3 is detected from the wireless tag.

The range defined by the thresholds TH3 and TH4 includes the maximumvalues of the received power strengths received from the wireless tagsprovided in a plurality of sheets being conveyed. Thus, it is possibleto prevent erroneous writing of information to non-target wireless tagsother than the target wireless tag.

FIG. 9 is a flowchart of the threshold determination processing carriedout by the controller 100. In order to convey the target sheet, thecontroller 100 transmits a conveyance start command to the printer unit18 (ACT301). The controller 100 receives the RSSI (R(0)) detected by thewireless tag communication device 201 through the communicationinterface 53 (ACT302). The controller 100 stores the time elapsed afterthe transmission of the conveyance start command and the acquired R(0)in the memory 52 in association with each other.

The controller 100 determines whether the conveyance of the target sheethas been completed (ACT304). When the conveyance has been completed, amessage indicating that the conveyance has ended is transmitted from theprinter unit 18 to the controller 100. The controller 100 can determinewhether the conveyance of the target sheet has been completed dependingon whether the message has been received.

If the conveyance has not ended (ACT304: NO), the controller 100acquires the RSSI again in ACT302. When the conveyance has beencompleted (ACT304: YES), the controller 100 determines whetherconveyance of a predetermined number of sheets has been completed(ACT305). The predetermined number of sheets is, for example, twosheets; however, the number of sheets used in this process is notparticularly limited, and, in general, the accuracy of the thresholdimproves with a greater number of sheets.

If the conveyance of the predetermined number of sheets has not beencompleted (ACT305: NO), the controller 100 transmits a conveyance startcommand to the printer unit 18 again in order to convey another targetsheet (ACT301). When the conveyance of the predetermined number ofsheets has been completed (ACT305: YES), the controller 100 determinesthe thresholds TH3 and TH4 (ACT306), stores the determined thresholds inthe memory 52 (ACT307), and ends the process. As described, ACT302 canbe repeated until a target sheet conveyance is completed. Therefore, aplurality of R(0) values can be acquired for each target sheet duringthe conveyance process. In an embodiment, the number of acquisitions ofthe RSSI value is about 10 during the transit of a target sheet throughthe image forming apparatus 10, but the number of acquisitions may beappropriately determined according to the expected variation of the RSSIor the like. Also, the number of sheets may be appropriatelypredetermined in accordance with the variation of the RSSI or the like.

The thresholds stored in the above-described threshold determinationprocessing are subsequently used in image formation processing. Thewireless tag control processing during image formation is performedaccording to the processing shown in FIG. 6. In the case of thethresholds shown in FIG. 8, the range of the ACT203 in FIG. 6 would berange [TH4, TH3], that is, greater than or equal to the threshold TH4and less than or equal to the threshold TH3.

As described above, in the second embodiment, it is possible to preventerroneous writing of information to a non-target wireless tag by usingthresholds determined in advance based on conveyance of a plurality ofsheets.

In the first and second embodiments, the magnitude of the output of theradio wave transmitted to the wireless tag by the wireless tagcommunication device 201 may be changed. The change in the magnitude ofthe output is effective, for example, in a case where the thresholdcannot be determined, or in a case where the threshold can be determinedbut the “range determined by the threshold” is too narrow to bepractical, for example. When the magnitude of the output is changeable,the controller 100 may determine the threshold by increasing ordecreasing the output. This makes it possible to improve the accuracy ofthe threshold, and thus it is possible to prevent erroneous writing ofinformation to non-target wireless tags other than the target wirelesstag.

In the first embodiment and the second embodiment, the controller 100performs the determination of the threshold and the instruction forwriting the information to the wireless tag, but the present disclosureis not limited to this. For example, the wireless tag communicationdevice 201 and a PC (Personal Computer) may be allowed to communicatewith each other, and the controller 100 and the PC can also communicatewith each other. The PC may thus perform the determination of thethreshold(s) and provide the instruction(s) for writing the informationto the wireless tag(s), and the controller 100 may more particularlyperform control related to conveyance of the sheet or the like. As such,as compared to a case where the processing is performed only by thecontroller 100, the processing load may be distributed, and generally,the PC has more computing resources. Therefore, it is possible toimprove the accuracy of the threshold evaluation by permitting a PC toperform statistical processing and fine control of wireless tag writingprocessing, and thus it is possible to additionally prevent erroneouswriting of information to a wireless tag other than the target wirelesstag.

The aforementioned embodiments prevent erroneous writing of informationto the non-target wireless tag by using the fact that the RSSI receivedfrom the wireless tag provided in a sheet being conveyed through animage forming apparatus changes. Accordingly, it is not necessary toprovide a special conveyance path for a sheet with a wireless tag to bewritten, and therefore, extra manufacturing cost and product cost arenot incurred. Furthermore, since it is not necessary to provide aspecial conveyance path, it is possible to install the wireless tagcommunication device in a general purpose image forming apparatus andupdate firmware or the like of the image forming apparatus to handlewireless tag writing operations. Therefore, it is possible to realizethe present embodiments at a very low cost without much additionaleffort beyond that already associated with the fabrication of an imageforming apparatus.

The functions of the image forming apparatus according to theabove-described embodiments may be realized by a computer. In such acase, one or more programs for performing the functions may be recordedin a non-transitory computer-readable recording medium, and the programsrecorded in the recording medium may be loaded into the computer systemand executed by the computer system. The “computer system” in thiscontext may include an operation system (OS) and hardware such as aperipheral device. A “computer-readable recording medium” refers to aportable medium such as a flexible disk, a magneto-optical disk, a ROM,or a CD-ROM, and a storage device such as a hard disk in the computersystem. Furthermore, the “computer-readable recording medium” may be anymedium for holding a program, and may be accessed by a communicationline and the program may be transmitted via a network such as theInternet or a communication line such as a telephone line. A program maybe downloaded, or otherwise transmitted, from a server or anothercomputer. Such server or other computer may be a cloud-based computer orthe like. The programs may perform a part of the functions describedabove, or may perform the above-described functions in combination withother programs already recorded in the computer system.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed:
 1. An image forming apparatus, comprising: a firstsheet storage unit in which a plurality of sheets each with a wirelesstag can be stored; a printer unit configured to convey a sheet along aconveyance path; a wireless tag communication device configured tocommunicate with wireless tags; and a controller configured to: controlthe printer unit to convey a first sheet along the conveyance path forimage formation, control the wireless tag communication device to detecta plurality of radio signal strengths from the first wireless tag duringthe conveyance of the first sheet and a plurality of radio signalstrengths for wireless tags of sheets not being conveyed by the printerunit, determine a threshold value of radio signal strength fordistinguishing a wireless tag on a sheet being conveyed along theconveyance path from wireless tags on sheets not being conveyed alongthe conveyance path based on the detected plurality of radio signalstrengths from the first wireless tag and the detected plurality ofradio signal strengths for wireless tags on sheets not being conveyed bythe printer unit, and control the printer unit to convey a second sheetand control the wireless tag communication device to write to a secondwireless tag on the second sheet when a radio signal strength from thesecond wireless tag is to equal or exceeds the threshold value.
 2. Theimage forming apparatus according to claim 1, wherein the thresholdvalue is greater than all of the radio signal strengths for wirelesstags on sheets not being conveyed by the printer unit.
 3. The imageforming apparatus according to claim 1, wherein the controller isfurther configured to: control the printer unit to convey a third sheetafter completion of the conveyance of the first sheet, and detect aplurality of radio signal strengths for a wireless tag on the thirdsheet during the conveyance of the third sheet, and the threshold valueis further determined using the detected plurality of radio signalstrengths from the wireless tag on the third sheet.
 4. The image formingapparatus according to claim 1, wherein the first sheet storage unit isa paper storage cassette.
 5. The image forming apparatus according toclaim 1, wherein the first sheet storage unit is a manual sheet feedtray.
 6. The image forming apparatus according to claim 1, wherein thefirst sheet storage unit is a sheet discharge tray.
 7. The image formingapparatus according to claim 1, further comprising: a second sheetstorage unit for storing sheets with wireless tags, wherein the firstsheet storage unit is a first paper storage cassette, and the secondsheet storage unit is a second paper storage cassette.
 8. The imageforming apparatus according to claim 1, further comprising: a secondsheet storage unit for storing sheets with wireless tags, wherein thefirst sheet storage unit is a paper storage cassette, and the secondsheet storage unit is sheet discharge tray.
 9. The image formingapparatus according to claim 1, wherein the wireless tag communicationdevice acquires, as first and second radio signal strengths, receivedsignal strength indicators (RSSIs).
 10. The image forming apparatusaccording to claim 1, wherein the wireless tag is a radio frequencyidentification (RFID) tag.
 11. A method for controlling an image formingapparatus, the method comprising: conveying a first sheet with a firstwireless tag along a conveyance path; acquiring a plurality of firststrengths for radio signals received from the first wireless tag duringthe conveyance of the first sheet; acquiring a plurality of secondstrengths of radio signals received from a second wireless tag of secondsheet of a first sheet storage unit during the conveyance of the firstsheet; determining a threshold value for distinguishing a sheet beingconveyed along the conveyance path from a sheet not being conveyed alongthe conveyance path based on the acquired first and second strengths;and conveying a third sheet and writing information to a third wirelesstag of the third sheet when a third strength of a radio signal receivedfrom the third wireless tag equals or exceeds the determined thresholdvalue.
 12. The method according to claim 11, wherein a maximum strengthof the first strengths exceeds each of the second strengths.
 13. Themethod according to claim 11, further comprising: after completion ofthe conveyance of the first sheet, conveying a fourth sheet, andacquiring a plurality of fourth strengths of radio signals received froma fourth wireless tag of the fourth sheet during the conveyance of thefourth sheet, wherein the threshold value is further determined based onthe fourth strengths.
 14. The method according to claim 11, wherein thethreshold value is greater than all of the strengths of radio signal forwireless tags on sheets not being conveyed by the printer unit.
 15. Themethod according to claim 11, wherein the first sheet storage unit is apaper storage cassette.
 16. The method according to claim 11, whereinthe first sheet storage unit is a manual sheet feed tray.
 17. The methodaccording to claim 15, wherein when a maximum of the first strengths isless than at least one strength of radio signals from wireless tags onsheets not being conveyed along the conveyance path.
 18. The methodaccording to claim 11, wherein received signal strength indicators(RSSIs) are acquired as the first and second strengths.
 19. The methodaccording to claim 11, wherein the wireless tag is a radio frequencyidentification (RFID) tag.
 20. A non-transitory computer readable mediumstoring a program that when executed causes an image forming apparatusto perform a method comprising: conveying a first sheet along aconveyance path; acquiring a plurality of first radio signal strengthsfrom a first wireless tag on the first sheet during the conveyance ofthe first sheet along the conveyance path; acquiring a plurality ofsecond radio signal strengths from wireless tags on sheets not beingconveyed along the conveyance path during the conveyance of the firstsheet; determining a threshold value of radio signal strength fordistinguishing a wireless tag on a sheet being conveyed along theconveyance path from wireless tags on sheets not being conveyed alongthe conveyance path based on the acquired first and second radio signalstrengths; and conveying a second sheet and then writing information toa second wireless tag on the second sheet when a radio signal strengthfrom the third wireless tag is equal to or exceeds the threshold value.